1. Field of the Invention
The present invention relates to a method for producing phosphates and phosphate-containing compounds, particularly alkaline earth phosphates, alkaline earth silicophosphates, or alkaline earth oxides.
2. Description of the Background Art
Phosphates play an important role in the production of various chemical products, such as, for example, fertilizers, detergent additives, food additives, feedstuffs, and corrosion inhibitors. In chemical terms, phosphates are salts and esters of orthophosphoric acid. Phosphates are extracted from volcanic or sedimentary deposits. Such reserves will be exhausted in the foreseeable future, however, so that a shortage of phosphate and rising prices can be expected. Therefore, efforts have been made increasingly to isolate phosphate from sewage sludge to assure a phosphate supply.
The main reserves of phosphates of natural origin are in northern Africa, Morocco, Western Sahara, the Kola Peninsula, Russia, Florida, South Africa, and China. There are also other reserves in Saudi Arabia; some other mining sites have already been exhausted.
As already mentioned, the aforementioned phosphate resources will be exhausted in the foreseeable future. There is also a major problem that most of these mineral sources are loaded with cadmium and other heavy metals. Many industrialized countries have already established a limit for the cadmium concentration in fertilizers. There is only one mining region, Kola, where the apatite falls below the permissible limit for cadmium and heavy metals in the European Community. As a result, the prices for phosphates and the products produced therefrom, particularly fertilizers, rise very greatly. The transition must therefore be made increasingly to using phosphates from uncontaminated sources.
The recovery of phosphates from sewage sludge, unfortunately, leads to unsatisfactory quantities and qualities. Furthermore, the time and effort to produce phosphates precipitated from sewage sludge, concentrated physically/biologically, and freed of (heavy) metals is very great and requires considerable energy.
It is known that bones and fish bones have a high mineral content and includes primarily of calcium and phosphate. The burning of bones or fish bones produces a grayish-white, porous bone ash, which has about 80% calcium phosphate, 6.6% calcium carbonate, and about 1.4% magnesium phosphate. These natural phosphate sources for the selective production of phosphate have not received attention thus far.
The production of phosphates from organic material is known. For comparison reference is made to publications DE 103 12 603 B4, DE 102 23 657 B4, DE 101 24 073 B4, DE 101 40 312 A1, DE 100 30 550 A1, or JP 2003-1761189, for example. These publications, however, either do not deal with the production of phosphates or describe one-step methods, which cannot be compared with the novel two-step method according to the present invention.